Question

Assume the random variable X has distribution X ~ Bin(9,0.5) and let Y = (-1)x. 1. Derive the probability mass function of Y. 2. Derive the mean of Y 3. Derive the variance of Y.
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Answer #1

Let's make table in excel:

From this table Y takes only two values as -1 and 1 The probability mass function of Y is as follows: P(x) 1 0.001953 1 0.017578 1 0.070313 1 0.164063 1 0.246094 10.246094 1 0.164063 1 0.070313 1 0.017578 1 0.001953 p(y) 0.5 0.5 6 4 0.5 0.5 y*p(y)p(x)*(y - mean)A2 0.5 0.5 0.5 0.5 0 10 12

b) Therefore mean of Y is 0

c) and variance of Y is 1

The formulae used on the above excel-sheet are as follows:

P(x) From this table Y tak The probability mass -1)AA2 BINOMDIST(A2,9,0.5,0) -1)AA3 BINOMDIST(A3,9,0.5,0) (-1)*A4 =BINOMDIST(A4,9,0.5,0) -1)MA5 BINOMDIST(A5,9,0.5,0) (-1)MA6BINOMDIST(A6,9,0.5,0) -1)AA7 BINOMDIST(A7,9,0.5,0) (-1)AA8 BINOMDIST(A8,9,0.5,0) -1)AA9 BINOMDIST(A9,9,0.5,0) -1)AA10 BINOMDIST(A10,9,0.5,0) -1)A11 BINOMDIST(A11,9,0.5,0) p(y) -C3+C5+C7+C9+C11 C2+C4+C6+C8+C10 p(y) 0.5 0.5 y p(y) p(x)*(y mean)A2 F8* (E8-0)A2 10 8 11 9 12 -SUM(G8:G9) SUM(H8:H9)

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